This invention relates to selective component agitation apparatus and method, e.g. apparatus for suspending the solid phase component in solid phase-containing reaction systems or reactants, particularly in assay reaction systems. The apparatus is particularly useful in automated assay machines. The invention further relates to a method for carrying out solid phase resuspension.
It is usual in, for example, hospital laboratories, to carry out large numbers of diagnostic reactions on samples from one or more subjects. Such reactions are conveniently carried out using automated assay machines, programmed to carry out the necessary tests and to display and/or issue the results in some hard copy form.
Usually such machines are provided with carriers, for example racks or carousels, which hold containers with the necessary reaction components for one or more specific diagnostic tests and/or the samples to be tested themselves.
Many assays, particularly where the assay is an immunoassay, have a solid component on which a particular reagent may be bound or adsorbed. In many cases the solid component is a particulate or finely divided solid phase which is capable of suspension in aqueous media. It is of course desirable, prior to using such solid phase components, to ensure that they are adequately suspended, thus preventing inaccuracies from being introduced into the assay.
It is known in the art to mix or resuspend components by vibratory methods, for example vibratory mixers are well known which operate by placing a sample container on a vibrating element, which causes mixing in the sample. One commercial immunoassay system uses a reaction container which is suspended at its top by a resilient "web". The base of the container is not suspended but hangs "free", and is adapted to interact with a mechanical agitator to transmit a disturbance to the whole container. In addition, EP 0051341 discloses an apparatus which includes a reagent/sample container-carrying carousel, which carousel is rotatable and has mounted thereon in fixed positions a number of individual containers.
In many systems found in the art, a problem with reactions which comprise a solid phase component is the cumulative effects of frequent resuspension and/or disturbance on the useful life of the solid phase reagent. After a time, solid phase components deteriorate due to fragmenting of particles or loss of bound reagent. This is a particular problem where, as is usually the case, a carousel carrier supports components for different tests, not all of which will be required for a particular patient sample, and some of which may be infrequently used and thus the corresponding reactants infrequently replenished. In such a situation, systems which vibrate or otherwise disturb the whole carousel carrier will cause resuspension of all solid phases carried thereon, regardless of whether or not these are needed for a particular reaction or test, leading to reactant deterioration and, ultimately, inaccurate or poor results. There are further problems in the art, in that suspension caused by vibration is unreliable and may also lead to inaccurate or poor results, and such a mixing or suspension made may result in undesirable aeration or frothing.